1. Field of the Invention
The present invention relates to a method of manufacturing high density silicon nitride sintered bodies having an excellent mechanical strength at high temperatures.
2. Related Art Statement
Up to this time, known various methods have been known for manufacturing high density silicon nitride sintered bodies having an excellent mechanical strength. As for one example, there is disclosed, in Japanese Patent Publication No. 61-25677, a method of manufacturing high density silicon nitride sintered bodies wherein a powder consisting essentially of powdery raw materials of silicon nitride and Y, Mg, Zr as sintering aids is formed to obtain a formed body, and the formed body is fired.
According to the known method mentioned above, it is possible to obtain the high density silicon nitride sintered bodies, but it is not possible to achieve a complete crystallization of an intergranular glass phase which affects a mechanical strength at high temperatures. Therefore, there is a drawback such that it is not possible to obtain certainly the silicon nitride sintered bodies having the excellent mechanical strength even at high temperatures.
In order to eliminate the drawback mentioned above, if a reheating treatment technique for crystallizing the intergranular glass phase disclosed in for example, Japanese Patent Publication No. 58-50944, is applied to the above silicon nitride sintered bodies, it is possible to obtain the silicon nitride sintered bodies having the excellent mechanical strength even at high temperatures. However, in this case, since the reheating treatment must be performed after firing the formed body, there is a drawback such that a manufacturing cost of the silicon nitride sintered bodies is increased.